Protection circuits



oct. 25,1927.

A. CARPE ET AL- PROTECTION CIRCUITS Filed Aug. 25. 1925 |NvENTvoRs pe BY- ATTORNEY Patented Oct. 25, 1927.

UNITED STATES PATENT OFFICE; g

ALLEN CARPE, oF NEW YORK, N."`Y.,"AND RALPH w. DEARDCRFF, or KENSINGTON,

CALIFORNIA, AssIGNoRs l'ro AMERICAN TELEPHONE kAND TRLEGRAPH COMPANY, I

A. CORPORATION OF NEW YORK.

PRorECTIoN CIRCUITS.

This invention relates to protective' apparatus and particularly to' apparatus for protectin y'circuits from high voltages.

In t 1e operation of telephone repeater circuits, particularly where it is desired to transfer from the output of the repeater considerable volumes of energy in order to bring the transmission up toa desired level, it is desirable to provide some means for protecting the outgoing Circuitfrom abnormal voltages as such abnormal voltages might be dangerous to the plant equipment and the maintenance forces. One of the objects of the invention is to provide suitable protective apparatus for such-an installation although the principle of the invention i-s applicable to the protection of other types of circuits.

The invention may now be more fully understood from the detailed description thereof when read Iin connection with the accompanying drawing, Figures 1, 2 and 3 of which illustrate circuit diagrams of three different embodiments of the invention.

Referring to'Fig. 1, L1 designates an incoming transmission line and L2 an outgoing transmission line at a repeater station, these l lines being interconnected through a high power amplifier stage A, comprising'vacuum tubes Vv and V arrangedy in the usual type of push-pull circuit. The input side of the amplifier A is connectedwith the `line L1 through transformer 11 and the output side of the amplifier is connected to the outgoing line L2 through transformer 12. In general, additional input amplifier stages willbe inv eluded in the incoming line L1, not shown in considered' that the total generated voltage must be equal to the voltage' drop, through the'internalimpedance of the amplifier plus -the voltage'fdrop through theimpedance of vthe line,- -The volta e drop 'across` the terminals of the line wlll be equal to the dropv L across the internal impedance of the repeater .tion opposite to the voltage of the' battery which is One-half uw aan drop. If the y1in@ should accidentally become open at some point, either due to a line failure, or due to the operation of a plug at thetest board or bv the blowing of' afuse or heat coil, the

entire applied voltage will appear across the terminals ofthe lines, or in other words,.the voltage across the line equipment will be doubled. If the alternating peak voltage is e Vnormally adjusted to be within the safety limits by a narrow margin, such opening of the circuit would cause the limits to be exceeded with consequent possible damage to equipment constituting a hazard from a fire standpoint and even a danger to the maintenance force. i I

Another potential source of abnormally high voltages in an installation of this kind arises from the'possibility of singing due to the large amount of amplification existing in the power amplifier and associated input amplifiers in tandem. It is well known that a'relatively small degree of unbalance orfeed-back between the output and input circuits of such an amplifier installation vmay cause the amplifiers to generate oscillations,

vwhose amplitude may greatly exceed they normal output of the amplifiers. ,Sjuch' effects-may arise due to line troubles,`etc.

In order to eliminate these dangers a rectifier tube R is provided which is bridged across the circuit of the line L2 through 'a .transformer 13. Circuit with the rectifier and is so poled that sov A battery C is Connected in it tends to cause a flow of current in the di-v f rection opposite to that for which the rectif` fier tube is conductive. As a consequence n current can fiow through the rectifier untili the @voltage peaks applied throughthe transformer 13 attain an amplitude greater than the voltage of the battery C. The half'.

waves of alternating voltage having a direc will then cause current to ow'through the rectifier R and through the winding of a re-v lay 14. 'If the voltage through the trans-l former 1exceeds 'the voltage of the battery ioo C by a's'iici-ent amount, enough current willv flow through the relay 14- to cause itto 4attract its armature. The current thus drawn -from the line tendsto reduce the' volta-ge facts as. ai protection. `,Furthermore,v the operation of .the relay; isi-,sach esto' open the 'eir- The relay 14 may have its circuit sov arv ranged that it will be locked up through a key K whereby when the voltage limits once have been exceeded the apparatus will operate automatically to open the output circuit and prevent the voltages from being applied negative to the line equipment. When once operated the circuit will remain in the condition just described until the trouble is located and repaired whereupon the key K may be opened to restore the relay 14 and the repeater circuit will function in the normal manner. 1

Fig. 2 illustrates a modified arrangement in which the protector circuit operates in response to abnormal voltages to disable the input side'ofthe repeatenev In this circuit, instead of using a rectifier R a threeelement vacuum tube R is employed. The filament of the tube obtains its current' from aI 2li-volt battery connection applied to a potentiometer asindicated. The resistance 15 of the potentiometer is in series with the filament of the tube. The grid of the tube is connected to the 24-volt lead through the resistance 16 of the potentiometer so that the grid is made with respect to the filament. The grid is made sufiiciently negative by this connection so that normally nocurrent can fiow i' vin the plate circuit due to the voltage of trated in the y120-volt B battery.

- `When, however, the voltages applied to the line L2 become abnormal, as. for example, when the repeater sings, or the line is opened, the positive lpeaks of the voltage will tend .to 'make the grid less negative and will permit current to flow in the plate cir'- cuit through the winding 17 of the relay 14. Therelay 17 when operated is locked up through lits winding 18 and the contact of I restoring key K, thereby maintaining a short circuit` connection at the upper` \co iitact of the relay 14 across the input circuit of the A amplifier. This prevents alternating voltage from being transmitted through the amplifier and conse uently protects the circuit L'2 from excess vo tage. When the trouble has been located. and -repaired the'restoring key K can be o rated to release the relay 17,

whereupon t e short circuit is removed and Athe re ater functions in a normal omanner.

A s 'glitlv modified arrangement is illus- Fig; 3.` In this figure the connection of the tube R to the output circuit i normally no current flows in the plate cir-A L2 is similar to that shown inFig. 2 andY cuit. When excess voltage is applied, how'- ever, the negative potential due to the. id battery Cis counteracted and current ows in the plate circuit and through the .wind- .l ing of the relay 14 .therebyenergizng said ,rjelay.'- Relay 14 turn closes a circuit .circuit of the amplifier A. The repeater is lo-peratea. relay, and means controlled by said amplifier, an out oing sai through relay 20 and through the restoringl key K. Relay 20 is locked up over'insiupper contact and over conductor 21 through the winding of the filament control relay 22. The filament control relay 22 is thereupon locked up in series with the relay 20, said relay 22 opening the filament circuit of the amplifier while at the same time relay 20 closes a short Acircuit across the input line L' Upon the condition causing the abnormal voltage being overcome the key K can 'be actuated, thereby releasing relays 20 and 22 to remove the short circuit from the incoming line L1 and to again close the filament now restored to normal condition and will function in the normal manner.

-It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as `defined in the following claims.`

What is claimed is:

1. In a protection system, a translating device, means to apply a voltage thereto to be translated, an outgoing circuit connected to said translating device, the impedance of the outgoing circuit being so related to the impedance of said translating device that the voltage across the outgoing circuit will normally be less than the translated voltage, means responsive to an increase inthe voltage drop across the` outgoing circuit to relay for preventing the abnormal voltage from being applied to the terminals of said outgoing circuit. l

2. In a' protection system, a translating device, means tn apply a potential thereto to be translated, an outgoing circuit connected to said translating device, the impedance of the outgoing circuit being so reated to the impedance of said translating device that the voltage drop across the termivvnals of the outgoing circuit will normally be less than the translated voltage, a vacuum tube connected to said outgoing circuit, means associated with said tube for preventing the current from flowing therethrough in'respponse to normal peakr voltages applied to the outgoing circuit but permitting current to fiow through said tube when the peak v voltages exceed'the normal flow, and a relay controlled by said tube and energized whencurrent flowsv therethrough to` prevent the excess voltages from being applied to the terminals of said outgoing circuit.

' 3. In a protection systemfor repeaters, an amplifier, an incomin circuit 'over which voltages may be applie to Saidcircuit connected v' the output'sde o am liier, a translatin device connected to sai outgoing circuit said 'translating device being so arran ai@ hohe I P a peaters comprising an amplifier, an incoming circuit over which voltages may be lapplied to said amplifier, an outgoing circuit con nected to the output side of said amplier, a vacuum tube connected to said output circuit, means associated with said tube for preventing current from 'flowing therethrough' when a normal voltage exists across the terminals of said outgoing circuit, but

permitting current to flow therethrough when said normal voltages are exceeded, and

means controlled by said vacuum tube in response to current flowing therethrough to prevent the abnormal voltages causing said.

current flow from being applied to the terminals of said outgoing circuit.

5. In a protection system Afor telephone repeaters, an amplifier', an incoming circuit over which voltages may be applied to saidV amplifier, an outgoing circuit connected to the 'output side of said amplifier, a vacuum 'tube connected to said outgoing circuit,"

means associated with said vacuum tube for preventing current flow therethrough'in re'- sponse to a normal voltage across said outgoing circuit but permitting current to flow through said tube when said normal voltage is exceeded, and a relay operated bycurrent flowing through said tube, said relay operatting to disable lsaid'amplifier.

6. In a protection system for telephoner repeaters, an amplifier, an incoming circuit over which voltages may be applied to said amplifier, an outgoing circuit connected to the output side of said amplifier, a vacuum tube connected to said outgoing circuit, means associated with said vacuum tube for preventing current flow therethrough in response to a normal voltage across said outgoing circuit but permitting current to flow through said tube when said normal voltage is exceeded, and a relay operated by current flowing through said tube, said relay operating to disable said incoming circuit.

7. In a protection system for telephone repeaters, an amplifier, an incomin circuit over which voltages may be applic to said amplifier, an outgoing circuit connected to the output side ot' said amplifier, a vacuum tube connected to said outgoing circuit, 'means associated with said vacuum tube for preventing current flow therethrough in response to a normal voltage across said outgoing circuit but permitting current to flow through said tube when said normal Voltage is exceeded, and a relay operated byvcurrent flowing through said tube, said relay operating to short circuit said incoming circuit. i 8. In a protection system for telephone repeaters, an amplifier, an incoming circuit over which voltages may be applied to said amplifier, an outgoing circuit connected to the output side of said amplifier, a vacuum tube connected to said outgoing circuit, means associated with said vacuum tube for preventing current flow therethrough in re- .sponse to a normal volta e across said outgoing circuit but permitting' currentto flow through said tube when said normal voltage is exceeded, and a relay operated by current flowing through said tube,'said relay operatving to disable said incoming circuit and todisable said amplifier. n

In testimony whereof, I have signed my name to this specification thisy 5th day of August, 1925.

ALLEN CARPE. In .testimony whereof, I have signed my name to this specification this 15th' day of August, 1925. K

. RALPH W. DEARDORFF. 

